Construction crews are erecting eight looming prototypes of President Trump's border wall in a remote section of the San Diego borderlands. Four are solid concrete; four are made of steel and concrete; one is topped with spikes. They all approach 30 feet in height. Customs and Border Protection is paying $20 million to six construction companies from Mississippi, Maryland, Alabama, Texas and Arizona. Crews in white hardhats operating cranes and forklifts are expected to complete the models by the end of the month.

Once the sections of wall are finished, CBP — parent agency of the Border Patrol — will evaluate them for three criteria.

"We want a better barrier. One that is hard to scale, hard to penetrate and hard to tunnel under," says Roy Villareal, chief of the San Diego Border Patrol sector.

"We're hoping innovation from private industry combined with our experience generates the next evolution of border security infrastructure," he continues.

About a half-dozen undocumented immigrants have been apprehended in the middle of the construction since the concrete slabs started going up. Most of them hopped over the 10-foot, Vietnam-era landing mats that currently serve as the primary border fence. The Border Patrol says, typically, it picks up about 70 illegal crossers in the entire San Diego sector every day.

While the mockups are massive, it's anybody's guess whether they'll ever get built. Trump's border wall is opposed by congressional Democrats and some Republicans, as well as most of California's and San Diego's leadership. But they're certainly getting lots of press. Every day, border agents in crisp green uniforms shuttle in news crews from as far away as the Czech Republic and the Netherlands to shoot video of the busy construction site just east of the Otay Mesa port of entry. The backdrops: south of the prototypes is a dusty Tijuana industrial zone; to the north are the rugged Otay Mountains.

"The real issue with building a border wall is what the Congress does, not what the contractors do ... The price tag on this is enormous," saysDoris Meissner, a former immigration commissioner and now a senior fellow at the nonpartisan Migration Policy Institute.

Moreover, with apprehensions of illegal crossers on the Southwest border at their lowest level in more than a decade, Congress may not feel the urgency to fortify the border. "As apprehensions continue to decline, it does become tougher to get the funding approval," says Victor Monjarrez, a former Border Patrol sector chief in Tucson, and currently associate director of the Center for Law and Human Behavior at the University of Texas at El Paso.

CBP expected the prototypes to spark big protests similar to the crowds that massed at the Standing Rock Sioux reservation in North Dakota last year decrying the pipeline. Officials even set aside a "free speech zone" and planned contingencies if trouble broke out. But since construction began three weeks ago, there have been no demonstrators.

"We knew this was political theater (from the Trump administration) and we're not going to respond," says Christian Ramirez, director of the Southern Border Communities Coalition in San Diego. "This is much ado about nothing." He says the much photographed prototypes represent "a guise that a border wall is being built" to please Trump supporters who chanted "Build the wall!" during the campaign.

On Tuesday, the president tweeted, "BORDER WALL prototypes underway!" above pictures of the massive sand-colored barriers. Sector Chief Roy Villareal declines to predict the future of the prototypes, or say whether they are, in fact, a model for a wall to be ultimately constructed somewhere along the southern frontier. "Part of the intent of the prototypes is to influence the ultimate design of new border fencing," he says. "[The final design] may well not be what you witnessed this morning." The administration has asked Congress for $1.6 billion for 74 miles of new border wall — most of it in south Texas. The request is pending as Congress considers larger border security and immigration legislation.

Over in Tijuana, Mexicans who live close to the international fenceline have mixed opinions regarding the concrete slabs rising on the other side.

"From the size of the wall they're building, they don't even want the wind to blow from there to over here," says Jose Avila Rodriguez, who runs a ramshackle recycling business in a dusty industrial district that faces the border. His wife, Juana, who is filling a large bag full of plastic bottles, has a different take.

"I don't think the new wall will deter people," she says. "How many years have they been crossing to the other side?"

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STEVE INSKEEP, HOST:

Prototypes of President Trump's proposed border wall are going up near San Diego. Each prototype is a little different. You can see the photos. One is a 30-foot-high slab of concrete and steel, another is a 30-foot-high slab of steel and concrete. Eight variations are all meant to pave the way for a wall that Congress has yet to fund. NPR's John Burnett is here for an architecture review. Hi, John.

JOHN BURNETT, BYLINE: Hi, Steve.

INSKEEP: So what's it like when you go down to the border and actually get a look at these things?

BURNETT: It's quite a scene. The Border Patrol has created this media bullpen at the edge of the construction site. And they've been shuttling in journalists from around the U.S. and around the world from as far away as Japan and Germany to see the great U.S.-Mexico border wall. You put on these fluorescent vests and hardhats and watch cranes lifting huge sections of sand-colored walls into place. They're massive, as you said - as tall as a three-story building.

INSKEEP: Well, the president had talked about innovative designs. At one point, he said maybe it should have solar panels, different ways to stop people from crossing the border. Did you see any innovations?

BURNETT: Nothing particularly artistic or high tech about these walls. One has elaborate spikes on top of it in case an illegal crosser has a really tall ladder.

INSKEEP: OK, well, I know you've spent time on both sides of the (laughter) border. Let's hear what people down there told you about it.

EDUARDO OLMOS: We're actually at the prototype site, San Diego sector, where eight of the prototypes are being built.

OLMOS: Once these are built, they're going to be evaluated for different characteristics like anti-climbing, anti-breaching, anti-scaling, anti-digging, anti-tunneling. Also, they have to be aesthetically pleasing.

BURNETT: The prototypes have all the appeal of blast walls. Some models are solid reinforced concrete. Others incorporate vertical steel posts. On the U.S. side, no one is allowed anywhere near the wall prototypes because of security precautions. To see what people think about them, I crossed the border at the Otay Mesa port of entry and worked my way over to the Los Torres neighborhood of Tijuana. There's a ramshackle recycling business here in Mexico that looks directly onto the soaring concrete slabs.

Jose Avila Rodriguez is pulling wires out of the dashboard of a wrecked truck.

JOSE AVILA RODRIGUEZ: (Speaking Spanish).

BURNETT: "From the size of the wall they're building, they don't even want the wind to blow from there to over here," he says ruefully. His granddaughter Melanie plays with puppies in the dusty street. Her grandmother Juana fills a bag with plastic bottles and considers Trump's border wall.

JUANA: (Speaking Spanish).

BURNETT: "I don't think the new wall will deter people," she says. "How many years have they been crossing to the other side?" Border Patrol officials in San Diego say they need some kind of new obstacle. Illegal crossers have cut 1,700 holes in the existing steel mesh fencing in the past three years. Just in the past three weeks, a half-dozen Mexican men have been nabbed in the construction zone while the prototypes were going up. Roy Villareal is the chief patrol agent here.

ROY VILLAREAL: What we want is something that is better, that is, again, impenetrable, unscalable and not capable of being dug under very quickly.

BURNETT: Six construction companies that won a nationwide competition to design and build the prototypes have until the end of this month to finish the eight mockups. I asked Villareal after his agency selects its favorite designs, does he believe these giant barriers will actually go up along the 2,000-mile frontier? He doesn't want to be pinned down.

VILLAREAL: These prototypes are going to influence the next evolution of our border infrastructure. So it very well may not be what you witness this morning.

BURNETT: Border Patrol officials are not waiting for a new wall design. The chief in the Rio Grande Valley of Texas told me he's planning to build 60 new miles of barriers, if Congress funds it, but he'll use what's there now - rust-colored steel columns that rise no higher than 18 feet. The administration has asked Congress for $1.6 billion for the first segments of the president's border wall.

But it faces a number of obstacles. It's opposed by congressional Democrats as well as most of California's and San Diego's leadership. And lawmakers in Washington are being hit with billions in unforeseen spending for hurricane damages from Texas to Puerto Rico. Doris Meissner, a former immigration commissioner and now a senior fellow at the nonpartisan Migration Policy Institute, thinks prospects for funding the wall look dim.

DORIS MEISSNER: The real issue with building a wall is what the Congress does, not what the contractors do. And the price tag on this is enormous.

BURNETT: The Border Patrol expected the prototypes to spark big protests. But since construction began, there have been no demonstrations.

CHRISTIAN RAMIREZ: We knew that this was political theater and that we weren't going to respond. This is much ado about nothing.

BURNETT: That's Christian Ramirez, director of the Southern Border Communities Coalition in San Diego, which has organized local rallies against Trump's immigration policies but not this time.

INSKEEP: So what are they doing instead, John Burnett?

BURNETT: Well, Ramirez thinks the real fight is in Washington. And that's where Congress will decide what to do about funding the border wall and what to do about the nearly 800,000 dreamers, the immigrants who were brought into this country illegally as children.

INSKEEP: OK. I guess we should mention that while activists have been relatively quiet, they think it's much ado about nothing, President Trump seems kind of excited.

BURNETT: Exactly. On Tuesday, the president tweeted a picture of those massive barriers with the message border wall prototypes underway.